Los Angeles: Legendary boxer Muhammad Ali, regarded as the greatest of all time by many and an inspiration for millions across the world, passed away late on Friday after being hospitalised with respiratory problems earlier this week. "After a 32-year battle with Parkinson's disease, Muhammad Ali has passed away at the age of 74," family spokesman Bob Gunnell said in a statement on Friday. Ali had been hospitalised in Phoenix, Arizona this week due to respiratory problems, although his condition was said to be stable. Paradise Valley Police Department in Arizona told ABC network an emergency medical call was made from Ali's address in Phoenix on Thursday, reports Efe. The Phoenix Fire Department also confirmed responding to a call on the same day to assist a 74-year-old man with respiratory issues. The legendary boxer had been hospitalized several times in recent years, including in early 2015 with a severe urinary infection that was initially diagnosed as pneumonia. "A true great has left us. Muhammad Ali transformed this country and impacted the world with his spirit," said Bob Arum, his long time boxing promoter. Ali was not a mere boxer, he was much more. Adored by millions around the globe, he was not loved for his amazing boxing skills alone, more for his beliefs. His fearlessness gave the blacks the confidence to fight for their rights. Born on January 17, 1942 Cassius Marcellus Clay in Louisville, a small town in Kentucky alongside the Ohio River, Ali was the first to win the world heavyweight title three times. Brash and witty, Ali had the unique ability and towering self-belief to back his words with his deeds. His pugilistic might was spread over three different decades and his record of 56-5 with 37 knockouts tells it all. Ali, known as Cassius Clay before he converted to Islam, first shot to global fame by winning the light-heavyweight gold at the 1960 Rome Olympics. Ali became world champion at 22 by defeating the seemingly unbeatable Sonny Liston. But one of the most defining moments of Ali's life came in 1967 when his Muslim faith and his strong conviction to stand up for his beliefs cost him dearly when he refused conscription to join the US Army during the Vietnam War. He was stripped of his title and his boxing license was also suspended by the state of New York. He was convicted of draft evasion and sentenced to five years in prison and a $10,000 fine. He paid a bond and remained free while the verdict was being appealed. Denied a boxing license in every state and stripped of his passport, Ali did not fight when he was in the prime of his physical power -- from age 25 to almost 29. However, his opposition to the Vietnam war and his anti-racism stance eventually endeared him to millions across the world and made him an iconic figure. As news of his death spread, tributes flowed in from all over the world. Celebrities in sports took to Twitter, Instagram and Facebook to pay their tributes to the legendary boxer. "God came for his champion. So long great one. @MuhammadAli #TheGreatest #RIP," former world heavyweight champion Mike Tyson tweeted. Former World champion Lennox Lewis tweeted, "A giant among men, Ali displayed a greatness in talent, courage & conviction, that most of us will ever be able to truly comprehend. #RIPAli" Recalling his playing days, former Olympic gold medallist and two-time world heavyweight champion George Foreman, who lost to Ali in the famous 'Rumble in the Jungle' in Zaire, said, "Ralph Ali, Frazier & Foreman we were 1 guy. A part of me slipped away, 'The greatest piece'." Former world champion boxer Manny Pacquiao tweeted, "Please keep @MuhammadAli in your thoughts and prayers. With God, all things are possible." Pacquiao's nemesis Floyd Mayweather took to Instagram to pour his heart out, "Today my heart goes out to a pioneer, a true legend, and a hero by all means! Your charisma, your charm and above all, your class are all of the elements that will be greatly missed by myself and the world." "You are someone that inspired me greatly throughout my boxing journey and words can not express how great you were as a person! Thank you for everything you've done for Black America, in the the world of sports & entertainment and for the legacy you leave behind! My sincerest condolences to the Ali family!" he added. Past and present stars from other sports also expressed their condolences. "The sporting universe has just suffered a big loss. Muhammad Ali was my friend, my idol, my hero. We spent many moments together and always kept a good connection throughout the years. The sadness is overwhelming. I wish him peace with God. And I send love and strength to his family," Brazil legend Pele, who is regarded as the greatest ever footballer along with Argentine legend Diego Maradona, wrote on his official Facebook page. Bollywood personalities also paid tributes to the former world champion. "Mohammed Ali the greatest ever! A gentleman and learned mind! He not just fought in the ring but outside it as well! And won! With the 'greatest' Muhammed Ali at his home in Los Angeles. Prakash Mehra had wished to make film with him and me," Amitabh Bachchan tweeted. "A legend no more - Muhammed Ali...Had the privilege of meeting him on a flight to London with my niece, Rachana. She is a big fan and insisted on this picture," noted singer Lata Mangeshkar, who shared an old photograph of herself with Ali, wrote on her Twitter handle. Finally allowed to continue his boxing career in 1970, Ali was beaten for the first time in his professional career by the legendary Joe Frazier in 1971 in what was termed as the 'Fight of the Century' in New York. However, Ali bounced back from that defeat and regained the world championship title with an eighth round knockout of reigning champion George Foreman. Ali fought Frazier for a third and final time in the Philippines on October 1, 1975, coming out on top in the "Thrilla in Manila". It was a brutal fight which tested the physical and psychological limits of both boxers. Ali was declared the winner when Frazier failed to emerge for the 15th and final round. Ali retired in 1981 and soon found signs of sluggishness and neurological damage. He thereafter received treatment for Parkinson's disease.